Lithium-ion secondary battery

Abstract

A lithium-ion secondary battery 100 includes a positive electrode current collector 221 and a porous positive electrode active material layer 223 retained by the positive electrode current collector 221 . The positive electrode active material layer 223 contains, for example, positive electrode active material particles 610 , an electrically conductive material 620 , and a binder 630 . In this lithium-ion secondary battery 100 , the positive electrode active material particles 610 have a shell portion 612 constituted by a lithium transition metal oxide, a hollow portion 614 formed inside the shell portion 612 , and a through hole 616 penetrating the shell portion 612 . In the lithium-ion secondary battery 100 , in the positive electrode active material layer 223 on average, the hollow portion 614 accounts for 23% or higher of an apparent sectional area of the positive electrode active material particles 610 . In addition, a thickness of the shell portion 612 in the positive electrode active material layer 223 on average is 2.2 μm or less.

The invention claimed is: 
     
       1. A lithium-ion secondary battery comprising:
 a current collector; and 
 a porous positive electrode active material layer which is retained by the current collector and which contains positive electrode active material particles, an electrically conductive material, and a binder, wherein 
 the positive electrode active material particles have: 
 a shell portion constituted by a lithium transition metal oxide; 
 a hollow portion formed inside the shell portion; and 
 a through hole that penetrates the shell portion, 
 in the positive electrode active material layer on average, the hollow portion accounts for 23% or higher of an apparent sectional area of the positive electrode active material particles, and 
 when a thickness of the shell portion at any position on an inner surface of the shell portion on any cross section of the positive electrode active material layer is defined as a shortest distance from the any position on the inner surface of the shell portion to an outer surface of the shell portion, a thickness of the shell portion in the positive electrode active material layer on average is 2.2 μm or less. 
 
     
     
       2. The lithium-ion secondary battery according to  claim 1 , wherein
 in the positive electrode active material layer on average, 
 the thickness of the shell portion is 0.05 μm or more. 
 
     
     
       3. The lithium-ion secondary battery according to  claim 1 , wherein the lithium transition metal oxide is a compound which has a layered structure and which contains nickel as a constituent element. 
     
     
       4. The lithium-ion secondary battery according to  claim 1 , wherein the lithium transition metal oxide is a compound which has a layered structure and which contains nickel, cobalt, and manganese as constituent elements. 
     
     
       5. The lithium-ion secondary battery according to  claim 1 , wherein the lithium transition metal oxide is a compound which has a layered structure and which is expressed as Li 1+x Ni y Co z Mn (1-y-z) M γ O 2 ,
 where 0≦x≦0.2, 0.1<y<0.9, 0.1<z<0.4, 
 M denotes an additive, and 0≦γ≦0.01. 
 
     
     
       6. The lithium-ion secondary battery according to  claim 5 , wherein the M is at least one additive selected from the group consisting of Zr, W, Mg, Ca, Na, Fe, Cr, Zn, Si, Sn, Al, B, and F. 
     
     
       7. The lithium-ion secondary battery according to  claim 1 , wherein a rated capacity is 3 Ah or higher. 
     
     
       8. The lithium-ion secondary battery according to  claim 1 , wherein the positive electrode active material particles are positive electrode active material particles produced by a production method comprising:
 a raw material hydroxide formation step of supplying ammonium ions to an aqueous solution of a transition metal compound, and precipitating particles of the transition metal hydroxide from the aqueous solution, with this aqueous solution containing at least one transition metal element that composes the lithium transition metal oxide; 
 a mixing step of mixing the transition metal hydroxide with a lithium compound to prepare an unfired mixture; and 
 a calcining step of calcining the mixture to obtain the active material particles. 
 
     
     
       9. The lithium-ion secondary battery according to  claim 8 , wherein
 the raw material hydroxide formation step includes: 
 a nucleation stage in which the transition metal hydroxide is precipitated from the aqueous solution; and 
 a particle growth stage in which the transition metal hydroxide is grown in a state where a pH of the aqueous solution is lowered from the nucleation stage. 
 
     
     
       10. The lithium-ion secondary battery according to  claim 9 , wherein
 a pH of the aqueous solution in the nucleation stage is 12 to 13, and 
 a pH of the aqueous solution in the particle growth stage is 11 or higher and lower than 12. 
 
     
     
       11. The lithium-ion secondary battery according to  claim 10 , wherein
 an ammonium ion concentration in the aqueous solution in the nucleation stage is 20 g/L or lower, and 
 an ammonium ion concentration in the aqueous solution in the particle growth stage is 10 g/L or lower. 
 
     
     
       12. The lithium-ion secondary battery according to  claim 11 , wherein the ammonium ion concentration of the aqueous solution in the nucleation stage and the particle growth stage is 3 g/L or higher. 
     
     
       13. Granules of the positive electrode active material particles used in the lithium-ion secondary battery according to  claim 1 .